Biochemical and X-ray structural analyses of the sources of specificity and fidelity in protein synthesis are being made through studies of tRNA, aminoacyl tRNA synthetases, base pairing and codon-anticodon interactons. BIBLIOGRAPHIC REFERENCES: J.R. Fresco & M.D. Topal, Base Pairing and Fidelity in Biological Processes. Abstracts, 1976 Spring Am. Chem. Soc. 100th Anniversary Symp. M.D. Topal & J.R. Fresco, - Complementary Base Pairing and the Origin of Substitution Mutations, Nature, 263, 285 (1976).